Variable speed condenser fan control system

ABSTRACT

A controller comprises a first input that receives a signal indicating an energy consumption value of a compressor, a second input that receives a signal indicating an energy consumption value of a variable speed condenser fan, and an output that provides a control signal to the variable speed condenser fan. The controller also comprises a memory that stores a condenser set point, and a processor in communication with the input, output and memory and that modulates the condenser set-point to minimize energy consumption and controls the variable speed condenser fan based on the condenser set-point.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/623,148 filed on Oct. 28, 2004. The disclosure of the aboveapplication is incorporated herein by reference.

FIELD

The present teachings relate to refrigeration systems and, moreparticularly, to a refrigeration system controller.

BACKGROUND

Refrigerated and frozen food product travels from processing plants toretailers, where the food product remains on display case shelves for anadditional period of time. In general, the display case shelves are partof a refrigeration system for storing and displaying the refrigeratedand frozen food product, which should be constantly cooled to ensuremaximum product life. In the interest of efficiency, retailers attemptto maximize the shelf-life and quality of the stored food product whileconcurrently maximizing the efficiency of the refrigeration system. Inso doing, retailers receive a profit through sales of quality productswhile minimizing spending on energy costs associated with productdisplay (i.e., refrigeration, etc.).

The refrigeration system plays a key role in controlling the quality ofthe food product. Thus, any breakdown in the refrigeration system orvariation in performance may cause food quality issues. Thus, it isimportant for the retailer to monitor the equipment of the refrigerationsystem to ensure it operates at expected levels.

Refrigeration systems generally require a significant amount of energyto operate. Therefore, energy requirements are a significant cost toretailers, especially when compounding energy uses across multipleretail locations. As a result, it is in the best interest of retailersto closely monitor performance of their refrigeration systems tomaximize efficiency and reduce operational costs.

Monitoring refrigeration system performance and energy consumption aretedious and time-consuming operations. Generally speaking, retailerslack the expertise to accurately analyze time and temperature data andrelate that data to food-product quality, as well as the expertise tomonitor the refrigeration system for performance and efficiency. Forexample, retailers typically set refrigerated display cases at lowerthan necessary temperatures to protect against a breakdown or stoppageof the refrigeration system. The cooler temperatures keep the foodproduct on display therein at a lower temperature, and thus, allow theretailer more time to repair the refrigeration system before the foodproduct may spoil.

Decreasing the temperature of the food product translates directly intoan increase in energy consumption as refrigeration components such ascompressors, evaporator fans, and condenser fans draw more energy toreduce the temperature within the display case. As can be appreciated,consuming more energy results in higher energy costs. Because theincrease in energy consumption does not necessarily lead to animprovement in the quality or safety of the food product itself,retailers cannot typically pass this additional cost to their customersand thus lose profit.

SUMMARY

A controller comprising a first input, a second input, an output, amemory and a processor is provided. The first input receives a signalindicating an energy consumption value of a compressor. The second inputreceives a signal indicating an energy consumption value of at least onevariable speed condenser fan. The output provides a control signal tothe variable speed condenser fan. The memory stores a condenserset-point. The processor is in communication with the input, output andmemory and modulates the condenser set-point to minimize energyconsumption. The processor controls the variable speed condenser fanbased on the condenser set-point.

In other features, the variable speed condenser fan is driven by avariable frequency drive. The control signal indicates a frequency ofelectrical power for the variable frequency drive to deliver to anelectric motor of the at least one variable speed condenser fan.

Further areas of applicability of the present teachings will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples areintended for purposes of illustration only and are not intended to limitthe scope of the teachings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present teachings will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of an exemplary refrigeration system;

FIG. 2 is a flowchart illustrating an initialization algorithm for avariable frequency condenser fan drive;

FIG. 3 is a flowchart illustrating a condenser fan control algorithmbased on a temperature difference set-point;

FIG. 4 is a flowchart illustrating a condenser fan control algorithmbased on a condenser temperature set-point;

FIG. 5 is a flowchart illustrating a condenser fan control algorithmbased on a condenser pressure set-point;

FIG. 6 is a flowchart illustrating a condenser fan control algorithm formodulating a temperature difference set-point;

FIG. 7 is a flowchart illustrating a condenser fan control algorithm formodulating a condenser temperature set-point;

FIG. 8 is a flowchart illustrating a condenser fan control algorithm formodulating a condenser pressure set-point;

FIG. 9 is a flowchart illustrating a condenser fan control algorithmbased on modulating a condenser fan capacity.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is in no wayintended to limit the teachings, its application, or uses. As usedherein, the terms module, control module, and controller refer to anapplication specific integrated circuit (ASIC), an electronic circuit, aprocessor (shared, dedicated, or group) and memory that execute one ormore software or firmware programs, a combinational logic circuit,and/or other suitable components that provide the describedfunctionality. Further, as used herein, computer-readable medium refersto any medium capable of storing data for a computer. Computer-readablemedium may include, but is not limited to, CD-ROM, floppy disk, magnetictape, other magnetic medium capable of storing data, memory, RAM, ROM,PROM, EPROM, EEPROM, flash memory, punch cards, dip switches, or anyother medium capable of storing data for a computer.

With reference to FIG. 1, an exemplary refrigeration system 10 includesa plurality of refrigeration cases 12, as well as a plurality ofcompressors 14 piped together with a common suction manifold 16 and adischarge header 18 positioned within a compressor rack 20. A dischargeoutput of each compressor 14 includes a respective compressortemperature sensor 24. An input to the suction manifold 16 includes botha suction pressure sensor 28 and a suction temperature sensor 30.Further, a discharge outlet of the discharge header 18 includes anassociated compressor discharge pressure sensor 34. As described infurther detail hereinbelow, the various sensors are implemented forcontrolling the refrigeration system components and evaluating energyrequirements for the refrigeration system 10.

The compressor rack 20 compresses refrigerant vapor that is delivered toa condenser 36 where the refrigerant vapor is liquefied at highpressure, thereby rejecting heat to the outside air. Condenser fans 38are associated with the condenser 36 to enable improved heat transferfrom the condenser 36. The condenser 36 includes an associated ambienttemperature sensor 40, a condenser temperature sensor 41, and acondenser discharge pressure sensor 42. The liquid refrigerant exitingthe condenser 36 is delivered to the plurality of refrigeration cases 12by way of piping 44. Each refrigeration case 12 is arranged in separatecircuits consisting of a plurality of refrigeration cases 12.

FIG. 1 illustrates two circuits labeled A and B. Each circuit is shownconsisting of four refrigeration cases 12. However, those skilled in theart will recognize that any number of circuits, as well as any number ofrefrigeration cases 12 within a circuit, may be employed. Each circuitwill generally operate within a certain temperature range. For example,circuit A may be for frozen food, circuit B may be for dairy, etc.

Because the temperature requirement is different for each circuit, eachcircuit includes a pressure regulator 46 that acts to control theevaporator pressure and, hence, the temperature of the refrigeratedspace in the refrigeration cases 12. The pressure regulators 46 can beelectronically or mechanically controlled. Each refrigeration case 12also includes its own evaporator 48 and its own expansion valve 50 thatmay be either a mechanical or an electronic valve for controlling thesuperheat of the refrigerant. In this regard, refrigerant is deliveredby piping 44 to the evaporator 48 in each refrigeration case 12.

The refrigerant passes through the expansion valve 50 where a pressuredrop causes the high pressure liquid refrigerant to achieve a lowerpressure combination of liquid and vapor. As hot air from therefrigeration case 12 moves across the evaporator 48, the low pressureliquid turns into gas, thereby removing heat from the refrigeration case12. This low pressure gas is delivered to the pressure regulator 46associated with that particular circuit. At the pressure regulator 46,the pressure is dropped as the gas returns to the compressor rack 20. Atthe compressor rack 20, the low pressure gas is again compressed to ahigh pressure gas, which is delivered to the condenser 36. The condenser36 creates a high pressure liquid to supply to the expansion valve 50 tostart the refrigeration cycle again.

A system controller 52 is used and configured or programmed to controlthe operation of the refrigeration system 10. The system controller 52is preferably an Einstein Area Controller offered by CPC, Inc. ofAtlanta, Ga., or any other type of programmable controller that may beprogrammed, as discussed herein. The system controller 52 operatesaccording to computer executable instructions contained on acomputer-readable medium 53 that may be local to the system controller52 or located remotely. The system controller 52 controls the bank ofcompressors 14 in the compressor rack 20, as well as the condenser fans38 to provide the desired suction pressure and to drive the condenserfans 38 at an optimum speed based on system performance. The systemcontroller 52 may include a processor in communication with memory, suchas RAM, ROM, EPROM, EEPROM, etc., that operate to control the condenserfans 38 and compressors 14. Operating data, such as a condenserset-point, may be stored by the system controller 52 in memory.

A separate case controller 55, such as a CC-100 case controller, alsooffered by CPC, Inc. of Atlanta, Ga. may be used to control thesuperheat of the refrigerant to each refrigeration case 12, via anelectronic expansion valve in each refrigeration case 12 by way of acommunication network or bus. A mechanical expansion valve may be usedwithout separate case controller 55. Should separate case controllers 55be utilized, the system controller 52 may be used to configure eachseparate case controller, also via the communication bus. Thecommunication bus may be a RS-485 communication bus, a LonWorks Echelonbus, or other suitable communication bus that enables the systemcontroller 52 and the separate case controllers 55 to receiveinformation from each refrigeration case 12.

Each refrigeration case 12 may have a temperature sensor 56 associatedtherewith. The temperature sensor 56 can be electronically or wirelesslyconnected to the system controller 52, the case controller 55, or theexpansion valve 50 for the refrigeration case 12. Each refrigerationcase 12 in the circuit may have a separate temperature sensor 56 to takeaverage/min/max temperatures. Alternatively, a single temperature sensor56 in one refrigeration case 12 within the circuit may be used tocontrol each refrigeration case 12 in the circuit since all of therefrigeration cases 12 in a given circuit operate at substantially thesame temperature range.

Compressor current sensors 58 generate compressor current signalscorresponding to the electrical current of each compressor. Thecompressor current signals are received by the system controller 52.Alternatively, electrical power meters may be used, in place ofelectrical current sensors, to generate signals corresponding toelectrical power, for example in kilowatt-hours, being used by eachcompressor 14. As can be appreciated, other units can be used for energyconsumption measurements. Moreover, any other suitable energy sensingdevice may be used to monitor energy consumption of the compressor. Ascan be further appreciated, any other suitable parameter correspondingto energy consumption may be used. For example, a control signal thatdirects the component to operate at a given level, such as a PID controlsignal. The control signal may direct the component to operate at adesired percentage of maximum operation. The system controller 52 maycalculate energy consumption based on the control signal and knowncharacteristics of the component.

The condenser fans 38 are variable-speed fans with electric, motors 39that are driven by a variable frequency drive unit (VFD) 60, such as aCommander SE, offered by Control Techniques, of Minneapolis, Minn. Theelectric motors 39 may be single-phase, or three-phase, AC synchronousmotors. As can be appreciated, other suitable adjustable speed drivesmay be used to drive the electric motors 39 of the condenser fans 38 atvarying speeds. The condenser fan speed is directly correlated to thefrequency delivered by the VFD 60. The VFD 60 receives electrical powerof a given frequency, e.g., sixty hertz, from a power source 62. Thepower source 62 may deliver single, or polyphase, electric powersuitable for the electric motors 39. For example, the power source 62may deliver 3-phase sixty hertz electrical power to the VFD 60.

FIG. 1 depicts four condenser fans 38 with electric motors 39 connectedto a single VFD 60. As can be appreciated, other electric motor 39 andVFD 60 configurations may be used. Any number of electric motors 39 maybe connected to any number of VFD's 60.

The VFD 60 has bypass 64 and frequency modulator 66 modules controlledby a VFD controller 68. The VFD 60 may be operated in variable frequencydrive mode (i.e., VFD-mode) or bypass-mode. In VFD-mode, electricalpower is delivered to the electric motors 39 from the frequencymodulator 66. In bypass-mode, electrical power is delivered from thebypass 64. In either mode, the VFD controller 68 selectively activatesthe electric motors 39, either at a variable frequency (VFD-mode), or ata fixed frequency (bypass-mode), in response to the system controller52.

In VFD-mode, electrical power is passed around the bypass 64 to thefrequency modulator 66 which delivers electrical power, at a desiredfrequency, to the electric motors 39. In bypass-mode, electrical poweris delivered directly to the electric motors 39 by the bypass 64, whichdelivers electrical power that matches the frequency of the power source62.

The frequency modulator 66 includes solid state electronics to modulatethe frequency of the electrical power. Generally, the frequencymodulator 66 converts the electrical power from AC to DC, and thenconverts the electrical power from DC back to AC at a desired frequency.For example, the frequency modulator 66 may directly rectify theelectrical power with a full-wave rectifier bridge. The frequencymodulator 66 may then chop the electrical power using insulated gatebipolar transistors (IGBT's) or thyristors to achieve the desiredfrequency. Other suitable electronic components may be used to modulatethe frequency of electrical power from the power source 62.

Electric motor speed of each electric motor 39 is controlled by thefrequency of the electrical power received from either the bypass 64 orthe frequency modulator 66. In bypass mode, the electric motors 39 mayreceive 60 hertz power, resulting in full capacity operation. InVFD-mode, the electric motor capacity varies with the receivedelectrical frequency. For example, at 30 hertz, the electric motors 39operate at half capacity operation.

The VFD 60 includes a heat-sink temperature sensor 72 that generates aheat-sink temperature of the VFD 60. Modulating the frequency ofelectrical power results in some power loss in the form of heat. The VFDcontroller 68 monitors the heat-sink temperature. When the heat-sinktemperature is above a predetermined heat-sink maximum temperature, theVFD 60 may be switched to bypass mode to allow the VFD 60 to cool.Additionally, the VFD 60 may be switched to bypass mode during periodsof high ambient temperatures as well.

The VFD controller 68 controls the output frequency of the frequencymodulator 66 and monitors various VFD 60 operating parameters. The VFDcontroller 68 monitors the electrical current and power drawn by each ofthe electric motors 39. Electrical current and power data is readilyavailable to the VFD controller 68 from the frequency modulator 66, asthe frequency modulator 66 generates the data while electronicallymanipulating the electrical power frequency. The monitored operatingparameter data is stored by the VFD controller in RAM 70 accessible tothe VFD controller 68. As can be appreciated, other computer-readablemedium suitable for reading and writing data may be used instead of RAM70. The operating parameter data is used by the VFD controller 68 duringVFD operation.

Referring now to FIG. 2, certain electric motor 39 characteristics aredetermined on startup. The VFD 60 has electrical relays for eachconnected electric motor. On startup, the system controller 52 directsthe VFD controller 68 to test each electric motor 39 individually todetermine the number of condenser fans present, and the horsepower ofeach. In step 200, the VFD controller 68 determines the number ofconnected electric motors.

In step 202, the VFD controller, 68 cycles the relays for each electricmotor 39, individually. In other words, the VFD controller 68 turns eachelectric motor 39 on one at a time. The VFD controller 68 monitors, andrecords, the electrical current drawn by each electric motor 39 duringthe test in step 204. This data is communicated to the system controller52. In step 206, the system controller 52 calculates the horsepower ofeach electric motor 39 based on the electrical current drawn during thetest. In step 208, when additional electric motors 39 remain to betested, the VFD controller 68 loops back to step 202.

The system controller 52 controls condenser fan 38 staging based on thestartup data, including the number of fans and horsepower data. As canbe appreciated, one, or all, of the startup algorithm steps may beexecuted by the system controller 52, the VFD controller 68, or acombination of system controller 52 and VFD controller 68.

Further, the system controller 52 uses the startup data to detect asystem malfunction during operation of the refrigeration system 10. Forexample, if a condenser fan 38 draws more electrical current thanexpected, the condenser 36 may be dirty or clogged. In such case, thesystem controller 52 may generate a notification of such. Additionally,if a condenser fan 38 does not draw enough current, the condenser fan 38may be malfunctioning, and an appropriate notification may be generated.

The VFD 60 receives, stores, or communicates other VFD 60 operating dataas well. For example, the frequency modulator 66 may encounter a faultcondition involving the frequency modulator 66 electronics which mayrequire maintenance. When the VFD controller 68 receives a faultcondition, the VFD 60 is switched to bypass-mode. Further, as describedabove, when a high heat-sink temperature is encountered, the VFD 60 isswitched to bypass mode.

When the VFD 60 is operating at, or near, full capacity, the VFD 60 isswitched to bypass mode. In such case, because the desired frequency isat or near the frequency of electrical power delivered by the powersource 62, there is no reason for the VFD 60 to modulate the frequency.

Other data may be programmed into the VFD controller 68 duringmanufacture or installation. For example, VFD model or serial numberinformation may be stored by the VFD controller 68. In such case, asufficient amount of non-volatile memory may be included on the VFD.Additionally, the size of the condenser fans 38 may be received by theVFD controller 68 at installation.

The system controller 52 communicates with the VFD controller 68 via acommunication link, such as a ModBus, a RS-485 communication bus, aLonWorks Echelon bus, or other suitable network communication connectionallowing digital data transfer. The communication link may be wired orwireless.

Traditionally, communications with the VFD 60 were made by way of ananalog data connection. By communicating with the VFD controller 68 viaa digital data connection, the system controller 52 is able to monitorthe operation of the condenser fans 38 by monitoring condenser fanoperation data contained in the VFD 60. More specifically, the systemcontroller 52 is able to monitor the output frequencies, andconsequently, the condenser fan 38 speeds. Further, the systemcontroller 52 is able to monitor the electrical power and current data,i.e., energy consumption information, for each of the electric motors39.

The system controller 52 monitors fault condition data from the VFDcontroller 68 as well. The system controller 52 is able to reset the VFDcontroller 68, and VFD electronics by way of a reset command to the VFDcontroller 68.

The system controller 52 monitors the energy consumption information ofboth the condenser 36, via the VFD controller 68, and the compressors14, via the compressor current sensors 58. The energy consumptioninformation is used by the system controller 52 to optimize theperformance of the refrigeration system 10 to ensure that a desiredcooling capacity is provided in each refrigeration case 12 whileconsuming a minimum amount of energy. Specifically, the systemcontroller 52 monitors the energy consumption of the compressors 14 andthe condenser 36 and controls condenser fan capacity to minimize thetotal energy consumption.

The system controller 52 may deliberately allow an increase in theenergy used by the condenser fans 36, in order to reduce the energy usedby the compressors 14 by a larger amount. In this way, the systemcontroller 52 optimizes the total power consumed by the compressors 14and condenser fans 36.

Condenser fan capacity refers to the cooling capacity of the condenserfans 38. In bypass-mode, the system controller 52 increases condenserfan capacity by turning one or more condenser fans 38 on, and decreasescondenser fan capacity by turning one or more condenser fans 38 off. InVFD-mode, the system controller 52 increases condenser fan capacity byincreasing the speed of one or more condenser fans, and decreasescondenser fan capacity by decreasing the speed of one or more condenserfans.

In both VFD-mode and bypass-mode, the system controller 52 is able toadjust condenser fan capacity by staging condenser fan operation basedon the horsepower of each of the electric motors 39 and based oncondenser fan size, if known. In other words, if a small increment incondenser fan capacity is needed, a low horsepower electric motor 39 ora small size condenser fan 38 may be activated. If a large increment incondenser fan capacity is needed, a high horsepower electric motor 39 ora large size condenser fan 38 may be activated. In VFD-mode, the systemcontroller 52 is also able to adjust condenser fan capacity by stagingcondenser fan operation based on condenser fan speed as well. If a smallincrement in condenser fan capacity is needed, a small increment to acondenser fan drive frequency is made. If a large increment in condenserfan capacity is needed, a large increment in a condenser fan drivefrequency is made.

The system controller 52 optimizes total energy consumption by changingthe condenser fan capacity and monitoring the corresponding change intotal energy consumption. In this way, the system controller 52 findsthe optimal condenser fan capacity.

The system controller 52 receives data from the respective temperature,pressure, and current sensors 24, 28, 30, 34, 40, 41, 42, 56, 58, anddata from the VFD controller 68. Specifically, the system controller 52receives: a suction pressure signal (P_(S)) generated by the suctionpressure sensor 28, a suction temperature signal (T_(S)) generated bythe suction temperature sensor 30, a compressor discharge pressuresignal (P_(D-Comp)) generated by the compressor discharge pressuresensor 34, an ambient temperature signal (TA) generated by the ambienttemperature sensor 40, a condenser temperature signal (T_(Cond))generated by the condenser temperature sensor 41, and a condenserdischarge pressure signal (P_(D-Cond)) generated by the condenserdischarge pressure sensor 42. Additionally, the system controller 52receives the compressor current signals from each of the compressorcurrent sensors 58, and calculates a total compressor electrical current(I_(Comp)). Also, the system controller 52 receives the condenser fancurrent signals, or data, from the VFD controller 68 and calculates atotal condenser fan electrical current (I_(Cond)). Because temperaturecan be calculated based on pressure, not all of the above sensors arenecessary. For example, the refrigeration system 10 may not include thecondenser temperature signal. In such case, the system controller 52 maycalculate T_(Cond) based on P_(D-Cond).

Generally, when condenser fan capacity is increased, P_(D-Cond) andP_(D-Comp) decrease. When condenser fan capacity is decreased,P_(D-Cond) and P_(D-Comp) increase. When P_(D-Comp) decreases, the loadon the compressor 14 is decreased, and, consequently, I_(Comp)decreases. At the same time, when condenser fan capacity is increased,I_(Cond) also increases. The system controller 52 adjusts condenser fancapacity to minimize the total energy consumption, i.e.,I_(Comp)+I_(Cond).

Condenser fan capacity may be controlled by a set-point. For example,the set-point may be a condenser temperature set-point (Tsp). In suchcase, the system controller 52 compares T_(Cond) with Tsp. When T_(Cond)is greater than Tsp, the system controller 52 increases condenser fancapacity and when T_(Cond) is less than Tsp, the system controller 52decreases condenser fan capacity. The set-point may also be a condenserpressure set-point (Psp). In such case, the system controller 52compares P_(D-Cond) to the Psp, and adjusts the condenser fan capacityas needed. Condenser fan control based solely condenser temperature orpressure set-points, however, does not account for varying ambienttemperatures.

The set-point may also be a temperature difference set-point (TD). Insuch case, the system controller 52 calculates a difference betweenT_(Cond) and TA and compares the difference to TD. Condenser fan controlbased on TD accounts for varying ambient temperatures. T_(Cond) isgenerally greater than TA. When the difference between T_(Cond) and TAis less than TD, the system controller 52 decreases condenser fancapacity. When the difference between _(TCond) and TA is greater thanTD, the system controller 52 increases fan capacity. Alternatively, thesystem controller 52 may calculate a difference between the ambienttemperature and a condenser discharge saturation temperature, which iscalculated based on the P_(D-Cond).

Traditional refrigeration systems operate based on a fixed set-point,i.e., fixed Tsp, Psp, or TD. In the traditional system, the set-pointremains constant despite varying refrigeration system loads and varyingoperating conditions.

The system controller 52 of the present teachings, on the other hand,modulates the condenser set-point to minimize total energy consumption.The system controller 52 varies the condenser set-point to adjust forvarying refrigeration system loads while minimizing total energyconsumption. The system controller 52 may store the condenser set-pointin memory accessible to the system controller 52.

The system controller 52 may modulate the condenser set-point within apredetermined operating range, including condenser maximum and minimumtemperatures. In this way, the system controller 52 insures thatT_(Cond) does not rise above a condenser temperature maximum. Forexample, when TD is used as the condenser set-point, T_(Cond) rises withTA. Thus, if TD is 10 degrees and TA is 80 degrees, the resultingT_(cond) may be 90 degrees. If TA rises to 90 degrees, the resultingT_(Cond) may rise to 100 degrees. When T_(Cond) reaches the condensertemperature maximum, the system controller 52 may simply controlcondenser fan capacity to lower T_(Cond), despite the TD set-point andthe rising TA. Further, the system controller 52 may check the condenserset-point against the condenser maximum and minimum temperatures eachtime the condenser set-point is modulated to insure the resultingT_(Cond) will be within the range.

Because T_(Cond) and P_(D-Cond) vary with TA, the pressure andtemperature of the refrigerant delivered to the refrigeration cases 12may also vary. The temperature of the refrigerated space in therefrigeration cases 12 is maintained, however, by operation of thepressure regulators 46 and the expansion valves 50.

With reference to FIG. 3, a control algorithm for adjusting condenserfan capacity based on a TD setpoint is executed by the system controller52. In step 350, the system controller 52 initializes the VFD 60.Initialization includes calculating the horsepower rating of eachelectric motor, as described above. In step 352, the system controller52 receives the VFD and condenser data from the VFD 60, such as,condenser fan size and electric motor horsepower.

In step 354, the system controller 52 determines whether a VFD fault hasoccurred. The fault may be an electronic fault, a high sink temperaturefault, or other system fault. When a fault is detected, operationproceeds in bypass-mode in step 356. When a fault is not detected,operation proceeds in VFD-mode in step 358. In step 360, the systemcontroller 352 compares the difference between T_(Cond) and TA with TD.When the difference is greater than TD, condenser fan capacity isincreased in step 362. When the difference is not greater than TD,condenser fan capacity is decreased in step 364. The system controller52 then loops back to step 354. The manner in which the condenser fancapacity is increased or decreased depends on the mode selected in step354. In bypass-mode, condenser fan capacity may be adjusted by turningan available condenser fan 38 on or off. In VFD-mode, condenser fancapacity may be adjusted by increasing or decreasing condenser fanspeed.

With reference to FIG. 4, a control algorithm for adjusting condenserfan capacity based on a Tsp set-point is executed by the systemcontroller 52. In step 470, the system controller 52 initializes the VFD60. In step 472, the system controller 52 receives the VFD and condenserdata from the VFD 60.

In step 474, the system controller 52 determines whether a VFD fault hasoccurred. When a fault is detected, operation proceeds in bypass-mode instep 476. When a fault is not detected, operation proceeds in VFD-modein step 478. In step 480, the system controller 52 compares T_(Cond)with Tsp. When T_(Cond) is greater than Tsp, condenser fan capacity isincreased in step 482. When T_(Cond) is not greater than Tsp, condenserfan capacity is decreased in step 484. The system controller 52 thenloops back to step 474. The manner in which the condenser fan capacityis increased or decreased depends on the mode selected in step 474.

With reference to FIG. 5, a control algorithm for adjusting condenserfan capacity based on a Psp set-point is executed by the systemcontroller 52. In step 570, the system controller 52 initializes the VFD60. In step 572, the system controller 52 receives the VFD and condenserdata from the VFD 60.

In step 574, the system controller 52 determines whether a VFD fault hasoccurred. When a fault is detected, operation proceeds in bypass-mode instep 576. When a fault is not detected, operation proceeds in VFD-modein step 578. In step 580, the system controller 52 compares P_(D-Cond)with Psp. When P_(D-Cond) is greater than Psp, condenser fan capacity isincreased in step 582. When P_(D-Cond) is not greater than Psp,condenser fan capacity is decreased in step 584. The system controller52 then loops back to step 574.

With reference to FIG. 6, a control algorithm 600 for optimizingcondenser fan capacity based on energy consumption using a TD setpointis executed by the system controller 52. The control algorithm 600 isstored on the computer readable medium 53 accessible to the systemcontroller 52. The system controller 52 includes time-keepingcapabilities, such as a system clock, or the like. In this way, thesystem controller 52 is able to monitor the current day and time.

The control algorithm 600 includes an iteration loop 602 that isexecuted based on daily and hourly time periods. As can be appreciated,other iteration loop periods may be used. For example, the iterationloop 602 may be executed on a number-of-minutes basis. In FIG. 6, days(d) start at d=0, and increase by 1 for each passing day. Hours (h)start at 0, and increase by 1 for each passing hour, 0 to 23.

The system controller 52 monitors TA and records an average ambienttemperature for a given hour of a given day (TA_(d,h)). Likewise, thesystem controller 52 monitors total current (i.e., I_(Comp)+I_(Cond))and records an average total current for a given hour of a given day(I_(d,h)). Other energy consumption indicators, such as totalkilowatt-hours, may alternatively be used. The system controller 52modulates and records the TD set-point for a given hour of a given day(TD_(d,h)).

The system controller 52 begins in step 604. In step 606, the first dayof operation, (i.e., d=0), TD_(d,h) for each hour (i.e. h=0 to 23) isinitialized to a predetermined initial value. The initial value may be10 degrees for all hours of the day. The system controller 52 thenrecords TA_(d,h) and I_(d,h) for each hour of the day.

In step 608, the second day of operation (i.e., d=1), the systemcontroller 52 changes TD_(d,h) for each hour (i.e., h=0 to 23) of theday. The change is for purposes of comparison between the first day andthe second-day, and may simply comprise incrementing TD_(d,h) by 1degree for each hour of the day. Alternatively, the change may comprisedecrementing TD_(d,h) by 1 degree for each hour of the day.

By the end of the second day, the system controller 52 has recorded afirst TD with corresponding ambient temperature and energy consumptiondata for each hour of the first day, and a second TD with correspondingambient temperature and energy consumption data for each hour of thesecond day. The system controller 52 can then determine whether thechange in TD increased or decreased total energy consumption for eachhour of the day. Generally, the system controller 52 calculates anamps-per-degree ratio (R) by dividing the total current for a given hour(i.e., I_(d,h)) by the average ambient temperature for the given hour(i.e., TA_(d,h)). By comparing the amps-per-degree ratio resulting fromdifferent TD's, the system controller 52 can determine whether a givenTD change increased or decreased the amps-per-degree ratio. Bycontrolling TD to minimize the amps-per-degree ratio, the systemcontroller 52 optimizes energy consumption of the refrigeration system.

As can be appreciated, other energy consumption indicators may be usedin place of amps. In which case, the appropriate energy-temperatureratio is used by the system controller 52.

On day 3 (i.e., d=2), the system controller 52 enters the iteration loop602. The loop is executed for each hour of the day. To set the TD_(d,h),the system controller 52 compares data from the same hour of theprevious 2 days.

In step 610, the system controller 52 calculates the amps-per-degreeratio for the same hour of the previous day:R_(d-1,h)=I_(d-1,h)/TA_(d-1,h).

In step 612, the system controller 52 calculates the amps-per-degreeratio for the same hour of the day before the previous day:R_(d-2,h)=I_(d-2,h)/TA_(d-2,h).

If the amps-per-degree ratio of the previous day is greater than theamps-per-degree ratio of 2 days ago, then the TD change between the 2days was in the wrong direction. In other words, the TD change resultedin higher amps-per degree. If, on the other hand, the amps-per-degreeratio of the previous day is less than the amps-per degree ratio of 2days ago, then the TD change was in the correct direction.

In step 614, the system controller 52 calculates a comparison factor (F)according to the formula: F=(R_(d-1,h−R) _(d-2,h))×(TD_(d-1,h−TD)_(d-2,h)).

Essentially, the system controller 52 adjusts the current TD based onwhether F is a positive or a negative number. For example, when energyconsumption increases, R_(d-1,h)−R_(d-2,h) will be a positive number.When energy consumption decreases, R_(d-1,h)−R_(d-2,h) will be anegative number.

Likewise, when TD was increased, TD_(d-1,h)−TD_(d-2,h) will be apositive number. When TD was decreased, TD_(d-1,h)−TD_(d-2,h) will be anegative number.

Further, when energy consumption increased, and TD was increased, F willbe positive, and TD should now be decreased. When energy consumptiondecreased, and TD decreased, F will be positive, and TD should now bedecreased. When energy consumption increased, and TD was decreased, Fwill be negative, and TD should now be increased. When energyconsumption decreased, and TD was increased, F will be negative, and TDshould now be increased. Because the sign of F is the crucialinformation (i.e., whether F is positive or negative), F may also becalculated as a quotient instead of a product.

In step 616, the system controller 52 determines whether F is ≧0. When Fis not ≧0, TD is decreased in step 618. In step 618, the systemcontroller 52 sets TD_(d,h) at TD_(d-1,h)−x, where x is an incrementalvalue. In step 618, x may be a predetermined constant, for example 0.5degrees, or 1.0 degree. Alternatively, x may be a calculated value thatdecreases over successive iterations of the iteration loop 602.

In step 616, when F is ≧0, TD is increased in step 620. In step 620, thesystem controller 52 sets TD_(d,h) at TD_(d-1,h)+x, where x is theincremental value.

In step 621, the system controller 52 checks TD against thepredetermined maximum and minimum condenser temperatures. If the TD willresult in a T_(Cond) outside of the predetermined range, then the TD isadjusted in step 621 so that the resulting T_(Cond) will be within thepredetermined range.

After setting TD_(d,h), the system controller 52 proceeds to step 622and records the current TD_(d,h), as well as the TA_(d,h) and I_(d,h)forthe hour. At the end of the current hour, the system controller 52proceeds again with step 610 and executes the iteration loop 602 again.

In this way, the system controller 52 optimizes the refrigeration system10 by continually monitoring energy consumption of the refrigerationsystem 10, continually changing the TD, and continually evaluating theeffect of the changed TD on energy consumption. The optimization occursfrom day-to-day on an hourly basis, such that data from a given hour ofthe day is compared with data from the same hour of previous days. Theoptimization accounts for the load variations throughout the day on therefrigeration system 10.

The optimization also accounts for any sensor inaccuracies that may bepresent in the system. As can be appreciated, temperature sensors,pressure sensors, and the like, may be inaccurate by some constantamount. For example, a temperature sensor may be inaccurate by 2 or 3degrees. A traditional system operating at a fixed temperaturedifference set-point will always operate at a temperature differenceset-point that is off by 2 or 3 degrees.

A refrigeration system 10 operated by the system controller 52 accordingto the control algorithm 600 will operate at the most efficienttemperature difference set-point, despite the inaccuracies of thetemperature sensor. For example, if the most efficient temperaturedifference set-point is actually 10 degrees, and if the condensertemperature sensor 41 is off by 2 degrees, the system controller 52 willfind the most efficient temperature difference set-point. To the systemcontroller 52, the most efficient temperature difference set-point willappear to be 12 degrees, or 8 degrees, due to the inaccurate condensertemperature sensor 41. But the system controller 52 will operate at themost efficient temperature difference set-point nonetheless. Thus, byexecution of the control algorithm 600, the system controller 52operates at the optimized temperature difference set-point, despite theinaccurate sensor.

The system controller 52 executing the control algorithm 600 may adjustTD_(d,h) within the T_(Cond) maximum range. In such case, the systemcontroller 52 may increase or decrease TD according to the controlalgorithm 600 until the resulting T_(Cond) maximum has been reached.

Referring now to FIG. 7, a control algorithm 700 for optimizingcondenser fan capacity based on energy consumption using a condensertemperature set-point (Tsp) is executed by the system controller 52. Thecontrol algorithm 700 is stored on the computer readable medium 53accessible to the system controller 52. The system controller 52 beginsin step 704. In step 706, the system controller 52 initializes theTsp's, and records TA_(d,h) and I_(d,h) for each hour of the first day.In step 708, the system controller 52 changes the Tsp's for each hour ofthe second day, and records TA_(d,h) and I_(d,h). The system controller52 then enters the iteration loop 702 starting with step 710.

As in the control algorithm 600 for TD, the system controller 52 in step710 calculates the amps-per-degree ratio of the previous day. In step712 the system controller 52 calculates the amps-per-degree ratio of 2days prior. In step 714, the system controller 52 calculates F accordingto the formula: F=(R_(d-1,h−R) _(d-2,h))×(Tsp_(d-1,h−Tsp) _(d-2,h)).

In step 716, the system controller 52 determines whether F is ≧0. When Fis not ≧0, Tsp is decreased in step 718. In step 718, the systemcontroller 52 sets Tsp_(d,h) at Tsp_(d-1,h)−x, where x is an incrementalvalue.

In step 716, when F is ≧0, Tsp is increased in step 720. In step 720,the system controller 52 sets Tsp_(d,h) at Tsp_(d-1,h)+x, where x is theincremental value.

In step 721, the system controller 52 checks the resulting Tsp againstthe condenser maximum and minimum temperatures. If the Tsp is outside ofthe predetermined range, the system controller 52 adjusts Tsp to withinthe predetermined range.

After setting Tsp_(d,h), the system controller 52 proceeds to step 722and records the current Tsp_(d,h), as well as the TA_(d,h) and I_(d,h)for the hour. At the end of the current hour, the system controller 52proceeds again with step 710 and executes the iteration loop 702 again.

In this way, the system controller 52 optimizes the refrigeration system10 by continually monitoring energy consumption of the refrigerationsystem 10, continually changing the Tsp, and continually evaluating theeffect of the changed Tsp on energy consumption.

Referring now to FIG. 8, a control algorithm 800 for optimizingcondenser fan capacity based on a condenser pressure set-point (Psp) isexecuted by the system controller 52. The control algorithm 800 isstored on the computer readable medium 53 accessible to the systemcontroller 52. The system controller 52 begins in step 804. In step 806,the system controller 52 initializes the Psp's, and records TA_(d,h) andI_(d,h) for each hour of the first day. In step 808, the systemcontroller 52 changes the Psp's for each hour of the second day, andrecords TA_(d,h) and I_(d,h). The system controller 52 then enters theiteration loop 802 starting with step 810.

As in the control algorithm 600 for TD, and the control algorithm 700for Tsp, the system controller 52 in step 810 calculates theamps-per-degree ratio of the previous day. In step 812 the systemcontroller 52 calculates the amps-per-degree ratio of 2 days prior. Instep 814, the system controller 52 calculates F according to theformula: F=(R_(d-1,h−R) _(d-2,h))×(Psp_(d-1,h−Psp) _(d-2,h)).

In step 816, the system controller 52 determines whether F is ≧0. When Fis not ≧0, Psp is decreased in step 818. In step 818, the systemcontroller 52 sets Psp_(d,h) at Psp_(d-1,h)−x, where x is an incrementalvalue.

In step 816, when F is ≧0, Psp is increased in step 820. In step 820,the system controller 52 sets Psp_(d,h) at Psp_(d-1,h)+x, where x is theincremental value. In step 821 the system controller 52 checks the Pspagainst the predetermined maximum and minimum condenser operatingpressures. If the Psp is outside of the predetermined range, the systemcontroller 52 adjusts Psp to within the predetermined range.

After setting Psp_(d,h), the system controller 52 proceeds to step 822and records the current Psp_(d,h), as well as the TA_(d,h) and I_(d,h)for the hour. At the end of the current hour, the system controller 52proceeds again with step 810 and executes the iteration loop 802 again.

In this way, the system controller 52 optimizes the refrigeration system10 by continually monitoring energy consumption of the refrigerationsystem 10, continually changing the Psp, and continually evaluating theeffect of the changed Psp on energy consumption.

Referring now to FIG. 9, a condenser fan control algorithm 900 utilizinga direct control of condenser fan capacity based on power consumption isexecuted by the system controller 52. In step 902, the system controller52 determines if the condenser fan capacity is at 100 percent. Whencondenser fan capacity is not at 100 percent, the system controller 52proceeds to step 904 and determines whether P_(D-Cond) is at the lowestsetting. When P_(D-Cond) is not at the lowest setting, the systemcontroller 52 increases condenser fan capacity in step 906 anddetermines whether the total electrical current (I) decreases in step908. When I decreases in step 908, the system controller 52 loops backto step 902.

In step 908 when I did not decrease, the system controller 52 proceedsto step 910 and determines whether condenser fan capacity is at 0percent. When condenser fan capacity is at 0 percent, the systemcontroller 52 loops back to step 902.

In step 902 when condenser fan capacity is at 100 percent, or in step904 when P_(D-Cond) is at the lowest setting, or in step 910 whencondenser fan capacity is not at 0 percent, the system controller 52reduces condenser fan capacity in step 912. In step 914, the systemcontroller 52 determines whether I decreased. When I decreased in step914, the system controller 52 loops back to step 910. When I did notdecrease, the system controller 52 loops back to step 902.

In this way, the system controller 52 adjusts condenser fan capacitybased on the current energy consumption of the refrigeration system 10.Energy consumption is optimized based on condenser discharge pressureand condenser fan capacity.

The description is merely exemplary in nature and, thus, variations thatdo not depart from the gist of the teachings are not to be regarded as adeparture from the spirit and scope of the teachings.

1. A controller comprising: a first input that receives a signalindicating an energy consumption value of a compressor; a second inputthat receives a signal indicating an energy consumption value of atleast one variable speed condenser fan; an output that provides acontrol signal to said at least one variable speed condenser fan; amemory that stores a condenser set-point; and a processor incommunication with said input, output and memory and that modulates saidcondenser set-point to minimize energy consumption and controls said atleast one variable speed condenser fan based on said condenserset-point.
 2. The controller of claim 1 wherein said at least onevariable speed condenser fan is driven by a variable frequency drive andwherein said control signal indicates a frequency of electrical powerfor said variable frequency drive to deliver to an electric motor ofsaid at least one variable speed condenser fan.
 3. The controller ofclaim 2 wherein said energy consumption value of said at least one ofcondenser fan comprises at least one of a condenser fan electricalcurrent value and a condenser fan electrical power value and whereinsaid energy consumption value of said at least one condenser fan isreceived from said variable frequency drive.
 4. The controller of claim2 wherein said processor determines a number of condenser fans connectedto said variable frequency drive based on said energy consumption valueof said at least one variable speed condenser fan.
 5. The controller ofclaim 2 wherein said processor determines a horsepower rating of saidelectric motor based on said energy consumption value of said at leastone variable speed condenser fan.
 6. The controller of claim 5 whereinsaid processor detects a condenser malfunction based on said horsepowerrating and based on said energy consumption value of said at least onevariable speed condenser fan.
 7. The controller of claim 2 wherein saidvariable frequency drive has a variable frequency mode wherein saidfrequency of electrical power is varied and a bypass mode wherein saidfrequency of electrical power is not varied.
 8. The controller of claim7 wherein said second input receives fault data from said variablefrequency drive and wherein said control signal triggers said variablefrequency drive to operate in said bypass mode when a variable frequencydrive fault occurs.
 9. The controller of claim 7 wherein said secondinput receives a signal indicating a variable frequency drivetemperature value and wherein said control signal triggers said variablefrequency drive to operate in said bypass mode when said variablefrequency drive temperature value is greater than a predeterminedvariable frequency drive temperature maximum.
 10. The controller ofclaim 7 wherein said control signal triggers said variable frequencydrive to operate in said bypass mode when operating said at least onecondenser fan at about full speed.
 11. The controller of claim 7 whereinsaid second input receives an ambient temperature value and wherein saidcontrol signal triggers said variable frequency drive to operate in saidbypass mode when said ambient temperature value is greater than apredetermined ambient temperature maximum.
 12. The controller of claim 2wherein said control signal triggers said variable frequency drive toreset.
 13. The controller of claim 2 wherein said set-point comprises atemperature difference set-point.
 14. The controller of claim 2 whereinsaid set-point comprises a condenser temperature set-point.
 15. Thecontroller of claim 2 wherein said set-point comprises a condenserpressure set-point.
 16. The controller of claim 2 wherein saidprocessor: sets said condenser set-point to an initial value; records afirst total energy consumption value resulting from said initial value;sets said condenser set-point to a different value; records a secondtotal energy consumption value resulting from said different value;compares said first total energy consumption value with said secondtotal energy consumption value; and modulates said condenser set-pointbased on said energy consumption comparison.
 17. The controller of claim16 wherein said first total energy consumption value corresponds tototal energy consumption during a predetermined period of a first dayand wherein said second total energy consumption value corresponds tototal energy consumption during said predetermined period of a secondday.
 18. The controller of claim 2 wherein said second input receives asignal indicating an ambient temperature value, and wherein saidprocessor: sets said condenser set-point to an initial value; records afirst total energy consumption value resulting from said initial value;sets said condenser set-point to a different value; records a secondtotal energy consumption value resulting from said different value;calculates a first energy-temperature ratio based on said first totalenergy consumption value and said ambient temperature value; calculatesa second energy-temperature ratio based on said second total energyconsumption value and said ambient temperature value; and modulates saidcondenser set-point based on said first and second energy-temperatureratios.
 19. The controller of claim 18 wherein said processor: comparessaid first energy-temperature ratio with said second energy-temperatureratio; and modulates said condenser set-point based on said ratiocomparison.
 20. The controller of claim 18 wherein said processor:calculates an energy ratio difference as a difference between said firstenergy-temperature ratio and said second energy-temperature ratio;calculates a set-point difference as a difference between said initialvalue and said different value; calculates a comparison factor as a oneof a product and a quotient of said energy ratio difference and saidset-point difference; and modulates said condenser set-point based onsaid comparison factor.
 21. The controller of claim 20 wherein saidprocessor determines a sign of said comparison factor and modulates saidcondenser set-point based on said sign.
 22. The controller of claim 2wherein said processor: sets said condenser set-point to an initialvalue; changes said condenser set-point in an initial direction; anddetermines a resulting energy consumption change; wherein said processorchanges said condenser set-point in an opposite direction of saidinitial direction when said resulting energy consumption change ispositive and changes said condenser set-point in said initial directionwhen said resulting energy consumption change is negative.
 23. A methodcomprising: monitoring an energy consumption of a compressor and atleast one variable speed condenser fan of a refrigeration system;controlling said at least one variable speed condenser fan based on acondenser set-point; and modulating said condenser set-point to minimizesaid energy consumption.
 24. The method of claim 23 wherein saidcontrolling said speed of said at least one variable-speed condenser fancomprises controlling a frequency of electrical power delivered by avariable frequency drive to an electric motor of said at least onevariable speed condenser fan.
 25. The method of claim 24 wherein saidmonitoring said energy consumption of said condenser comprises receivingat least one of electrical current data and electrical power data fromsaid variable frequency drive.
 26. The method of claim 23 furthercomprising: setting said condenser set-point to an initial value;recording a first energy consumption resulting from said initial value;setting said condenser set-point to a different value; recording asecond energy consumption resulting from said different value; comparingsaid first energy consumption with said second energy consumption; andmodulating said condenser set-point based on said energy consumptioncomparison.
 27. The method of claim 23 wherein said set-point comprisesone of a temperature difference set-point, a condenser temperatureset-point, and a condenser pressure set-point.
 28. The method of claim24 wherein said variable frequency drive has a variable frequency modeand a bypass mode, said method further comprising controlling saidfrequency of electrical power at a desired frequency when operating insaid variable frequency mode and controlling said frequency ofelectrical power at an input frequency when operating in said bypassmode.
 29. The method of claim 28 further comprising receiving fault datafrom said variable frequency drive.
 30. The method of claim 29 furthercomprising operating in said bypass mode when said fault data isreceived from said variable frequency drive.
 31. A computer-readablemedium having computer-executable instructions for performing the methodof claim
 23. 32. A computer-readable medium having computer-executableinstructions for performing the method of claim
 24. 33. Acomputer-readable medium having computer-executable instructions forperforming the method of claim
 25. 34. A computer-readable medium havingcomputer-executable instructions for performing the method of claim 26.